Hi team, I am triggering multiple VAPI calls from Make.com. 85% of my requests work as expected and we are calling the phone number with our agent. However about 15% of our calls for some reason return a Bad Request error and the call never goes through. Nothing changes structurally with my Post command other than the phone number (which is formatted correctly always). Is there any reason why a phone number couldn't be called and would give me a Bad Request error? Is there any way to confirm this is the case? Thank you!

Thank you for the details. To help diagnose the "Bad Request" errors, could you please share an example (with sensitive info redacted) of a phone number that fails, along with the exact error message or code you receive from VAPI for that request? Source: - [Outbound Calling Documentation](https://docs.vapi.ai/calls/outbound-calling)

here you go! This exact format is working for other calls. But some just don't work like the one below - { "assistantId": "xxxxx", "phoneNumberId": "xxxxx", "customer": { "number": "+1xxx7195978" }, "assistantOverrides": { "variableValues": { "agentName": "Paige", "firstName": "LEVI", "companyName": "xxx", "jobSource": "Indeed.com", "wednesday1":"August 6th, 2025", "wednesday2":"August 13th, 2025", "area": "Spokane, Washington" } } } Method POST HeadersArray 1Collection Key Content-Type Value application/json Handled error type RuntimeError message [400] Bad Request

Some phone numbers may be: Outside Vapi’s supported region list (e.g. blocked country). Carrier-restricted (e.g. premium, VOIP, or short codes). Improperly sanitized, even if they “look correct.”

is there any way to tell if this number is any of those?

First, normalize the number (+1XXXXXXXXXX). Run a lookup (Twilio/Telnyx) to confirm it’s valid and see the line type. If it’s valid but VOIP/ported, that’s likely why it rejects. If logs say “region not permitted”, you’ll need a Twilio number with the right permissions.

Hi Alex, For the "Bad Request" errors, check if the issue is linked to the call end reasons or logs for specific endedReason codes. The [Call Ended Reasons](https://docs.vapi.ai/calls/call-ended-reason) document has a list of possible errors. Also, make sure your API requests are properly formatted with valid parameters, as this can cause "Bad Request" errors. If the issue continues, reviewing your server's logs for detailed error messages can help identify the problem.